Partial oxidation of a hydrocarbonaceous feedstock, in particular hydrocarbons, in the presence of a catalyst is an attractive route for the preparation of mixtures of carbon monoxide and hydrogen, normally referred to as synthesis gas. The partial oxidation of hydrocarbons is an exothermic reaction represented by the equation:CnH2n+2+n/2O2→n CO+(n+1)H2
There is literature in abundance on the catalysts and the process conditions for the catalytic partial oxidation of hydrocarbons. Reference is made, for instance, to EP-A-303 438, U.S. Pat. No. 5,149,464, EP-B-576 096, WO 99/37380, and WO 99/19249.
In a catalytic partial oxidation process in a fixed catalyst bed, the temperature of the top layer, i.e. the layer at the upstream end of the catalyst bed, is typically higher than the temperature further downstream in the catalyst bed. This is due to the fact that the catalytic partial oxidation reaction is mass and heat transfer limited, i.e. full conversion is subject to mass and heat transfer limitations between the bulk of the gaseous feed mixture and the catalyst surface, and/or that some endothermic reforming reactions might occur in the downstream part of the catalyst bed.
High temperatures in the top layer of the catalyst are unwanted, since the rate of catalyst deactivation increases with temperature. Therefore, there is a need in the art for a catalytic partial oxidation process wherein the temperature in the top layer of the catalyst bed can be reduced.
In International Patent Application WO 01/46068, it was found that, in a process for the catalytic partial oxidation of a hydrocarbonaceous feedstock using a fixed bed catalyst, the temperature of the upstream part of the catalyst can be reduced by carrying out the process in a reactor retaining the fixed bed catalyst, which reactor is designed such that a part of the conversion product flows back to the zone just upstream of the catalyst bed.